Composite guidewire withdrawn and filled tube construction

ABSTRACT

The present invention is directed to an intracorporeal device, preferably a guidewire, and method for making the device. The guidewire of the present invention is formed, at least in part, of a composite elongate core formed, at least in part, of precipitation hardened material. The elongate core members of the present invention will have an ultimate tensile strength and modulus of elasticity greater than the same for an identically dimensioned elongate member formed from superelastic NITINOL alone.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 09/470,874, filed onDec. 22, 1999 which is a Continuation-In-Part of U.S. Ser. No.09/224,453, filed on Dec. 31, 1998 which issued on Nov. 7, 2000 as U.S.Pat. No. 6,142,975, the contents of which are hereby incorporated byreference.

FIELD OF INVENTION

This invention relates to the field of guidewires for advancingintraluminal devices such as stent delivery catheters, balloondilatation catheters, atherectomy catheters and the like within bodylumens.

BACKGROUND OF THE INVENTION

Conventional guidewires for angioplasty and other vascular proceduresusually comprise an elongated core member with one or more taperedsections near the distal end thereof and a flexible body such as ahelical coil disposed about the distal portion of the core member. Ashapeable member, which may be the distal extremity of the core memberor a separate shaping ribbon which is secured to the distal extremity ofthe core member extends through the flexible body and is secured to arounded tip at the distal end of the flexible body.

In a typical coronary procedure, a guiding catheter having a preformeddistal tip is percutaneously introduced into a patient's peripheralartery, e.g. femoral or brachial artery, by means of a conventionalSeldinger technique and advanced therein until the distal tip of theguiding catheter is seated in the ostium of a desired coronary artery. Aguidewire is positioned within an inner lumen of a dilatation catheterand then both are advanced through the guiding catheter to the distalend thereof. The guidewire is first advanced out of the distal end ofthe guiding catheter into the patient's coronary vasculature until thedistal end of the guidewire crosses a lesion to be dilated, then thedilatation catheter having an inflatable balloon on the distal portionthereof is advanced into the patient's coronary anatomy over thepreviously introduced guidewire until the balloon of the dilatationcatheter is properly positioned across the lesion. Once in positionacross the lesion, the procedure is performed.

A requirement for guidewires is that they have sufficient columnstrength to be pushed through a patient's vascular system or other bodylumen without kinking. However, guidewires must also be flexible enoughto avoid damaging the blood vessel or other body lumen through whichthey are advanced. Efforts have been made to improve both the strengthand flexibility of guidewires to make them more suitable for theirintended uses, but these two properties are for the most part,diametrically opposed to one another in that an increase in one usuallyinvolves a decrease in the other.

Further details of guidewires, and devices associated therewith forvarious interventional procedures can be found in U.S. Pat. No.4,748,986 (Morrison et al.); U.S. Pat. No. 4,538,622 (Samson et al.):U.S. Pat. No. 5,135,503 (Abrams); U.S. Pat. No. 5,341,818 (Abrams etal.); and U.S. Pat. No. 5,345,945 (Hodgson et al.); all of which areincorporated herein in their entirety by reference.

Some guidewires have been formed from a superelastic alloy such as aNITINOL (nickel-titanium or NiTi) alloy, to achieve both flexibility andstrength. When stress is applied to NITINOL alloy exhibitingsuperelastic characteristics at a temperature at or above which thetransformation of martensite phase to the austenite phase is complete,the specimen deforms elastically until it reaches a particular stresslevel where the alloy then undergoes a stress-induced phasetransformation from the austenite phase to the martensite phase. As thephase transformation proceeds, the alloy undergoes significant increasesin strain but with little or no corresponding increases in stress. Thestrain increases while the stress remains essentially constant until thetransformation of the austenite phase to the martensite phase iscomplete. Thereafter, further increase in stress are necessary to causefurther deformation.

If the load on the specimen is removed before any permanent deformationhas occurred, the martensitic phase of the specimen will elasticallyrecover and transform back to the austenite phase. The reduction instress first causes a decrease in strain. As stress reduction reachesthe level at which the martensite phase transforms back into theaustenite phase, the stress level in the specimen will remainessentially constant until the transformation back to the austenitephase is complete, i.e. there is significant recovery in strain withonly negligible corresponding stress reduction. After the transformationback to austenite is complete, further stress reduction results inelastic strain reduction. This ability to incur significant strain atrelatively constant stress upon the application of a load and to recoverfrom the deformation upon the removal of the load is commonly referredto as superelasticity. These properties to a large degree allow aguidewire core of a superelastic material to have both flexibility andstrength.

While the properties of the guidewire formed of the superelasticmaterial were very advantageous, it was found that the guidewires andguiding members formed of materials having superelastic characteristicsdid not have optimum push and torque characteristics.

SUMMARY OF THE INVENTION

The present invention is directed to an intracorporeal device,preferably a guidewire, and method for making the device. The guidewireof the present invention is formed, at least in part, of a compositeelongate core member formed, at least in part, of precipitation hardenedmaterial. The elongate core members of the present invention will havean ultimate tensile strength and modulus of elasticity greater than thesame for an identically dimensioned elongate member formed fromsuperelastic NITINOL alone.

Preferably, the composite elongate core member has a modulus ofelasticity of at least 9×10⁶ psi, more preferably, at least 12×10⁶ psi,and most preferably, at least 15×10⁶ psi.

Preferably, the composite elongate core member has a an ultimate tensilestrength of at least 150 ksi, more preferably, at least 180 ksi, andmost preferably, at least 200 ksi.

In one embodiment, the precipitation hardened material is formed from amaterial comprising at least two material selected from the groupconsisting of nickel, cobalt, molybdenum, chromium, tungsten, and iron.

In one embodiment, the precipitation hardened material is formed from aprecipitation hardenable stainless steel. Preferably, the precipitationhardenable stainless steel is chromium-nickel based single stagemartensitic precipitation hardenable stainless steel. In anotherembodiment, the precipitation hardenable stainless steel is essentiallynickel free.

In another embodiment, the precipitation hardened material is formedfrom a cobalt based alloy. In one embodiment the cobalt based alloyfurther includes nickel, molybdenum and chromium while in anotherembodiment it further includes less than about 10% by wt. iron.

In one preferred embodiment, the composite elongate core member has aninner core element and a first layer portion disposed at least in partabout the inner core element, the inner core element and the first layerportion being formed of different material. In an embodiment, the innercore element and the first layer portion are independently formed fromsuperelastic NITINOL and precipitation hardenable material. In anotherembodiment, the composite elongate core member further includes a secondlayer portion disposed at least in part about the first layer portionand formed of a material similar to the inner core element material.

In a preferred embodiment, the composite elongate core member includes adistal segment having a distally tapered section with proximal anddistal portions, and a distal flexible section, the inner core elementbeing at least partially exposed at the distal flexible section of thedistal segment of the composite elongate member.

As is known in the art, many materials used for guidewire constructionhave desirable mechanical properties, but are difficult to assemble toother guidewire components using conventional technology such assoldering or use of polymer adhesives due to inherent surface propertiessuch as tenacious oxide layers. The construction of guidewires accordingto the present invention allows the use of materials which have poorbondability or solderability.

The present invention allows for the design of a guidewire with aunitary core, rather than a core with proximal and distal segmentsjoined together. Additionally, the core members of the present inventionmay be used with other wire designs to create guidewires with improvedsuperelasticity and kink-resistance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross sectional view of a guidewire embodyingfeatures of the invention.

FIG. 2 is a transverse cross sectional view of the guidewire of FIG. 1taken along line 2-2.

FIG. 3 is a transverse cross sectional view of the guidewire of FIG. 1taken along line 3-3.

FIG. 4 is a diagrammatic illustration of a stress-strain curve.

FIG. 5 is a transverse cross sectional view of an alternative guidewireembodying another configuration.

FIG. 6 is a transverse cross sectional view of another alternativeguidewire embodying another configuration.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1, 2 and 3 illustrate features of a guidewire 10 embodying thepresent invention. A composite elongate core member 11 has a distalsegment 13 having a distally tapered section 16 with a proximal portion19, a distal portion 22, and a distal flexible section 25 at a distalend 28 of the guidewire 10 for negotiating the guidewire 10 through thepatient's vasculature without causing injury thereto. The distallytapered section 16 can be adjusted in length, taper angle and crosssectional shape to achieve the desired flexibility and performancecharacteristics for the guidewire 10.

The elongate core member 11 has an inner core element 31 formed from aprecipitation hardenable material, a first layer portion 37 formed froma superelastic material disposed on an outer surface 43 of the innercore element 31, and a second layer portion 46 formed from precipitationhardenable material disposed on an outer surface 52 of the first layerportion 37. The inner core element 31 is at least partially exposed atthe distal flexible section 25 of the distal segment 13 of the compositeelongate member 11. The inner core element 31 may also be exposed at adistal end 53 of the distal portion 22. The first layer portion 37 is atleast partially exposed at the distal portion 22 of the distally taperedsection 16 of the distal segment 13 of the composite elongate coremember 11.

In FIG. 1, The first layer portion 37 and second layer portion 46 areshown as smooth continuous layers. The inner core element 31 has aproximal section 55, a distal section 58 and a distal end 61. The firstlayer portion 37 has a distal section 64 and a proximal section 67. Thesecond layer portion 46 has a distal section 70 and a proximal section73.

The distal end 61 of the inner core element 31 is secured to a distalend 76 of a flexible body 79 by a first body of solder 82. A proximalend 85 of the flexible body 79 is secured to the distal section 70 ofthe second layer portion 46 with a second body of solder 88. Although asingle distally tapered section 16 is shown, the distal segment 13 ofthe elongate core member 11 may have two or more such tapered segmentswhich may or may not be separated by segments of substantially constantdiameter. The flexible body 79 is disposed partially about the distallytapered section 16 of the distal segment 13 of the elongate core member11. The distal flexible section 25 is shown as a flattened portion ofthe exposed inner core element 31, however, the distal flexible section25 can have a round cross section, or any other suitable configuration.

The flexible body 79 may be any flexible material such as a helical coilor, a polymer jacket, or the like. Polymers suitable for forming theflexible body 79 include, but are not limited to, polyimide,polyethylene, polyurethane, tetrafluoroethylene (TFE),polytetrafluoroethylene (PTFE), expanded polytetrafluoroethylene (PTFE),and other similar materials. The flexible body 79 in the form of ahelical coil 92 (as shown in FIG. 1) may be formed of a suitableradiopaque material such as tantalum, gold, iridium, platinum or alloysthereof or formed of other material such as stainless steel and coatedwith a radiopaque material such as gold. The wire from which the coil 92is made generally has a transverse diameter of about 0.001 to about0.004 inch, preferably about 0.002 to about 0.003 inch. Multiple turnsof a distal portion of coil 92 may be expanded to provide additionalflexibility. The flexible body 79 may have transverse dimensions aboutthe same as a proximal section 95 of the elongate core member 11. Theflexible body 79 may have a length of about 2 to about 40 cm or more,but typically will have a length of about 2 to about 10 cm.

The inner core element 31, at an untapered region such as the proximalsection 95 of the elongate core member 11, has a nominal transversedimension of up to about 0.010 inches, preferably, about 0.003 to about0.01 inches, and more preferably, about 0.003 to about 0.006 inches. Thefirst layer portion 37 and second layer portion 46, at an untaperedregion such as the proximal section 95 of the elongate core member 11,each have a nominal wall thickness of up to about 0.015 inches,preferably, about 0.0005 to about 0.01 inches, and more preferably,about 0.001 to about 0.003 inches. Although the inner core element 31 isshown as solid, the inner core element 31 may also be hollow with alumen extending longitudinally therethrough (not shown) for delivery ofdiagnostic or therapeutic agents, such as radioactive therapy agents orangiogenic growth factors or the like; or for advancement of elongatedmedical devices into a patient's vasculature.

The inner core element 31 and the second layer portion 46 may both beformed of precipitation hardened material formed from precipitationhardenable material, with the first layer portion 37 being formed from asuperelastic material such as superelastic NITINOL. However, asdiscussed below, other configurations may also be employed in thepractice of the invention.

A significant aspect of the invention resides in forming the compositeelongate core member 11, at least in part, from precipitation hardenablematerial so that the ultimate tensile strength (σ_(uts)) and tensileyield strength (σ_(ys)) of the composite (FIG. 4) are raised to enhancethe elastic strength and operability of the guidewire, as compared to anelongate core member formed of superelastic NiTi alone.

In an embodiment, features of which are illustrated in FIG. 5 andwherein like references refer to like parts, the guidewire 10′ has aninner core element 31′ formed from precipitation hardenable material(e.g., precipitation hardenable stainless steel) and a first layerportion 37′ formed from superelastic material (e.g., superelasticNITINOL).

In another embodiment, features of which are illustrated in FIG. 6 andwherein like references refer to like parts, the guidewire 10″ has aninner core element 31″ formed from superelastic material (e.g., NITINOL)and a first layer portion 37″ formed from precipitation hardenablematerial (e.g., precipitation hardenable stainless steel).

Materials suitable for use in the practice of the invention arecharacterized in that they are precipitation hardenable by controlledheat treatment, not only to increase the ultimate tensile strength ofthe material but also to increase the tensile yield strength.

The characteristics of the composite elongate core member 11 accordingto the present invention, without any intention to limit the scope ofthe invention, may be described as follows:

The ultimate tensile strength and the Young modulus of elasticity forthe composite elongated core member are proportional to the crosssectional area of each constituent multiplied by the ultimate tensilestrength or the modulus of elasticity, respectively, of thatconstituent, as defined in Equations I and II, respectively:σ_(uts(C))=[σ_(uts(S))×(A _((S)) /A _((C)))]+[σ_(uts(Co))×(A _((Co)) /A_((C)))]  Equation IE _((C)) =[E _((S))×(A _((S)) /A _((C)))]+[E _((Co))×(A _((Co)) /A_((C)))]  Equation IIwherein

-   -   σ_(uts) is the ultimate tensile strength,    -   E is the Young modulus of elasticity    -   A is the cross sectional area,    -   C is the composite member,    -   Co is the core,    -   S is the shell (the shell may, itself, comprise various layers,        such as the first and second layer portions).

The foregoing characteristics may be achieved by making the compositeelongate core member 11, in part, from a precipitation hardenablematerial. Example of such precipitation hardenable material include, butare not limited to, AISI (American Iron and Steel Institute) Type 600series precipitation hardenable stainless steel. Additional examplesinclude chromium-nickel based single stage martensitic precipitationhardenable stainless steel having modified proportions of chromium andnickel and with additional elements of copper and titanium, commerciallyavailable from Carpenter Steel Company of Reading, Pa., under thedesignation 455PH or 17-7PH; and a precipitation hardenable steelavailable under the trade designation 1RK91 from Sewden Steel.

Other suitable precipitation hardenable stainless steel include thosewhich are essentially “nickel free” such as those sold under thedesignation BioDur 108, available from Carpenter's Specialty AlloysOperations, Reading, Pa. By way of example, the nominal composition ofBioDur is chromium (21%), manganese (23%), nitrogen (1%), nickel (lessthan 0.3%), and iron (balance).

Other suitable precipitation hardenable material include cobalt basedalloys such as those including nickel, cobalt, molybdenum and chromium,also commercially available under the designation MP35N (UNS (UnifiedNumbering System) R30035) available from Carpenter Steel Co. Also usefulin the practice of the invention is a similar alloy that contains asmall amount of iron (less than about 10%) and is commercially availableunder the trade designation Elgiloy (UNS R30003) and L605 from HaynesInternational of Kokomo, In.

The material for forming the first layer portion 37 may be asuperelastic alloy, such as superelastic NITINOL (NiTi).

By way of example, the ultimate tensile strength and Young modulus forthe composite core member 11 according to FIG. 5, may be calculatedusing nominal and or preferred values for the ultimate tensile strengthand Young modulus for each of the constituents, using Equations I andII, above, and the following parameters:

-   -   C has an overall outer diameter of 0.0125 inch,    -   Co is precipitation hardenable stainless steel (PHSS),    -   % A_((Co))=6 to 20%, nominal 12%−equivalent to a core outer        diameter of about 0.0045 inch,    -   S is superelastic NiTi,    -   % A_((S))=94 to 80%, nominal 88%, equivalent to a shell wall        thickness of about 0.004 inch (0.008 inch total shell        thickness),    -   E_((Co))=28-30×10⁶ psi, nominal 28.5×10⁶ psi, for PHSS; and        33.5-35×10⁶ psi, nominal 34.5×10⁶ psi, for cobalt base alloys        such as MP35N, L605, and Elgiloy, with less than 10% Iron,    -   σ_(uts)(_(Co))=250-330 ksi, preferably ≧280 ksi,    -   E_((S))=9-13×10⁶ psi, nominal 12×10⁶ for NiTi,    -   σ_(uts(S))=160-190 ksi, preferably ≧175 ksi,    -   σ_(uts(C))=[σ_(uts(S))×(A_((S))/A_((C)))]+[σ_(uts(Co))×(A_((Co))/A_((C)))]    -   σ_(uts(C))=(0.88×175 ksi)+(0.12×280 ksi)=188 ksi    -   E_((C))=(0.88×12×10⁶ psi)+(0.12×28.5×10⁶ psi)=14×10⁶ psi

As can be seen from the equations and numbers above, the elongate coremembers of the present invention will have an ultimate tensile strengthand modulus of elasticity greater than the same for an identicallydimensioned elongate member formed from superelastic NITINOL alone.

The composite elongate core member 11 will preferably have an ultimatetensile strength of at least 150 ksi, more preferably, at least 180 ksi,and most preferably, at least 200 ksi; and a modulus of elasticitygreater than 9×10⁶ psi, more preferably, greater than 12×10⁶ psi, andmost preferably, greater than 15×10⁶ psi.

The following process is provided, by way of example and not aslimitation, to illustrate the method of forming the composite elongatecore member 11 of the guidewire 10 in accordance with the invention.

A NiTi alloy tube, for forming the first layer portion 37, having acomposition of about 55.9% Ni and 44.1% Ti was drawn to a diameter ofabout 0.060 inch and an inner diameter of about 0.024 inch. A wire of17-7PH precipitation hardenable stainless steel was formed with adiameter of about 0.020 inch for forming the inner core element 31. The17-7PH wire was inserted into the first layer portion 37. A tube of17-7PH was prepared with an inner diameter of about 0.068 inch and anouter diameter of about 0.114 inch for forming the second outer layerportion 46. The 17-7PH tube for the second layer portion 46 was disposedover the first layer portion 37 (NiTi tube) containing the inner coreelement 31 (17-7PH wire).

The entire assembly was then drawn in a series of five stages with a30-60% reduction in cross-sectional area followed by a heat treatmentbetween 600-800° C., in air for about 15 minutes, at each stage. Thefifth stage was followed by a sixth stage which included drawing withcold work of about 16% followed by heat treating at a temperaturebetween 400-600° C. and a seventh stage which included drawing with acold work of about 50% but with no heat treatment. The final cold workedproduct was aged at a temperature of about 650° C. for about one minuteto develop maximum bending, yield, and modulus with minimum springback.

It should be noted that other suitable methods may also be used. Forexample, the inner core element 31 and the first layer portion 37, andthe second layer portion 46, may have different dimensions.Alternatively, the inner core element 31 may be loaded into the firstlayer portion 37 and cold drawn down to a suitable size prior toinsertion into the second layer portion 46. The new assembly can then bedrawn down to the desired final size.

While particular forms of the invention have been illustrated anddescribed, it will be apparent that various modifications can be madewithout departing from the spirit and scope of the invention.Accordingly, it is not intended that the invention be limited, except asby the appended claims.

1. A heat-treated elongate member, comprising: a composite elongatecore; the composite elongate core including an inner core formed of aprecipitation hardened material concentrically surrounded by, anddirectly contacting and attached to, a first layer formed of asuperelastic material, the first layer having a proximal section anddistal section; a second layer formed from a precipitation hardenedmaterial concentrically arranged about at least the proximal section ofthe first layer; and a flexible body distinct from the first layer atleast partially overlying the distal section of the first layer.
 2. Theelongate member of claim 1 wherein the precipitation hardened materialused to form the inner core is precipitation hardened stainless steel.3. The elongate member of claim 2 wherein the precipitation hardenedmaterial used to form the inner core is chromium-nickel based singlestage martensitic precipitation hardened stainless steel.
 4. Theelongate member of claim 2 wherein the precipitation hardened stainlesssteel used to form the inner core includes less than 0.3% nickel.
 5. Theelongate member of claim 1 wherein the precipitation hardened materialused to form the inner core is a cobalt based precipitation hardenedalloy.
 6. The elongate member of claim 5 wherein the cobalt based alloyfurther includes nickel, molybdenum and chromium.
 7. The elongate memberof claim 1, wherein the composite elongate core includes a distalsegment having a distally tapered section with proximal and distalportions, and a distal flexible section, the inner core element being atleast partially exposed at the distal flexible section of the distalsegment of the composite elongate member.
 8. The elongate member ofclaim 1, wherein the elongate member is a guidewire.
 9. The elongatemember of 8 wherein the composite elongate core includes a distalsegment having a distally tapered section with proximal and distalportions, and a distal flexible section, the inner core element being atleast partially exposed at the distal flexible section of the distalsegment of the composite elongate member, and at least some of the firstlayer portion being at least substantially exposed at the proximalportion of the distally tapered section of the distal segment of thecomposite elongate core.
 10. The elongate member of claim 1 wherein theprecipitation hardened material comprises of at least two materialselected from the group consisting of nickel, cobalt, molybdenum,chromium, tungsten, and iron.
 11. The elongate member of claim 1 whereina portion of the flexible body is soldered to the second layer.
 12. Theelongate member of claim 1 wherein a portion of the flexible body issoldered to the inner core.
 13. The elongate member of claim 12 whereina portion of the flexible body is soldered to the second layer.
 14. Theelongate member of claim 1 wherein the inner core and second layer areformed from similar precipitation hardened materials.
 15. A guide wire,comprising: a composite elongate core; the composite elongate coreincluding an inner core formed of a precipitation hardened materialconcentrically surrounded by, and directly contacting and attached to, afirst layer formed of a superelastic material, the first layer having aproximal section and distal section; a flexible coil disposed at adistal end of the distal section of the first layer; a second layerformed from a precipitation hardened material concentrically arrangedabout at least the proximal section of the first layer; and wherein theprecipitation hardened material used to form the inner core andsuperelastic material extend from the proximal section of the firstlayer to at least through a part of a length of the flexible coil.
 16. Aheat-treated elongate member, comprising: a composite elongate core; thecomposite elongate core including an inner core formed of aprecipitation hardened material concentrically surrounded by, anddirectly contacting and attached to, a first layer formed of asuperelastic material, the first layer having a proximal section anddistal section; a flexible body disposed at a distal end of the distalsection of the first layer; the distal section having a proximal portionand a tapered distal portion; a second layer formed from a precipitationhardened material concentrically arranged about at least the proximalsection of the first layer; and wherein the precipitation hardenedmaterial used to form the inner core and superelastic material extendfrom the proximal section of the first layer to the tapered distalportion of the distal section of the first layer and continuing throughat least a part of a length of the flexible body.
 17. The elongatemember of claim 16 wherein a portion of the flexible body is soldered tothe second layer.
 18. The elongate member of claim 16 wherein a portionof the flexible body is soldered to the inner core.
 19. The elongatemember of claim 18 wherein a portion of the flexible body is soldered tothe second layer.
 20. The elongate member of claim 16 wherein the innercore and second layer are formed from similar precipitation hardenedmaterials.